1. Field of the Disclosure
The present disclosure relates to electronic devices and methods, and more particularly, to electronic devices including a plurality of singulated die and methods of forming the same.
2. Description of the Related Art
Electronic devices can include a plurality of die packaged together to reduce the area taken up on a board over the area that would be taken up if the die are conventionally packaged and mounted on the board separately. Within such a package, the die can be stacked to further reduce the board area covered by the package. By packaging the die as a die stack, some of the connections between the die of the stack, that would conventionally require a connection and trace on the board if the die were not stacked, can be included within the package as an intrastack connection. Thus, the number of connections between the stack and the package (extrastack connections) can be reduced by stacking and forming intrastack connections among a plurality of die within a package rather than mounting and forming connection to the die conventionally.
However, packages that include die stacks can be relatively thicker than other packages that include single die or a plurality of die that are not stacked. Thus, a package including a die stack can be a thickest package on a board and a limiting form factor for how thin a space the board can occupy.
Packaging such a die stack can also require special processing techniques or equipment. A machine designed for performing conventional packaging may not have the clearance to manipulate the thicker die stack. For example, a thickness dimension of a mold for encapsulating such a die stack can be larger than a tool for conventional encapsulation can accommodate. Also, the additional thickness of the die stack can require a thicker packaging substrate to accommodate a deeper cavity in the packaging substrate to control the bond pad elevation of the die stack relative to the packaging leads.
One method of reducing the thickness of a package having stacked die is to use bump die attach technology rather than wire bonding to form intrastack and extrastack electrical connections. However, without forming through vias in some of the die of the die stack, stacking die using bump die attach can be limited to a two-layer stack with the die oriented front side to front side. Additionally, at least one of the two die of the front-to-front die stack typically is significantly larger than the other die of the die stack to allow for extrastack connections to be made from the die stack. This difference in size and shape can make stacking die of a same type that typically have a same size and shape, more difficult, as different pad layout can be required.
In another method of reducing the thickness of the die stack, a die of the die stack is thinned after becoming a portion of the die stack, such that the overall thickness of the die stack is reduced by the amount of the thinning of the die. The intrastack connections of the die stack can stabilize the die as it is thinned. However, using the die stack in this way is more likely to damage the die stack than if the die of the die stack is not thinned.
One method that allows for the stacking two or more die includes forming a through via such that a front to back connection can be made through at least one of the die of the die stack. Thus, forming through vias can allow the die stack to be formed with all die oriented with front sides facing substantially the same direction (e.g. front side to back side), despite having substantially the same size and shape. Front-to-back orientation with through vias can extend the number of layers of die in the stack to more than two.
However, as the die are thinned to accommodate forming through vias, handling the substrate can become so problematic as to be impractical. Physical robustness and rigidity of the die substrates or wafer substrates from which die substrates are formed varies with the substrate thickness and the area. For example, a wafer substrate of less than 200 microns thick, or a die substrate of less than 100 microns can be so thin as to deform under a vacuum. Such deformation can make formation of reliable bump connections more difficult because the bumps are not maintained in a same plane during placement of the die.
Accordingly, the industry continues to demand improved processes for forming die stacks for microelectronic application that include thinner die and have reliably formed intrastack connections.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention. The use of the same reference symbols in different drawings indicates similar or identical items.